A southern perspective...
If you attend the shower, you bring a gift.
If you attend the wedding, you bring (or send) a gift.
If you attend both, you give presents for both. Two event, two gifts.
If you're invited to multiple showers, then you can be excused. Normally, the bride will say something along the lines of "I'd love you to be at my other shower, too, but please don't bring another gift. I really just want you to meet so-and-so who will be there!" Or whatever the reason is she wants you to attend more than one....
In our area, shower presents are usually smaller than wedding presents.
Personally, I spend $75-100 on weddings and around $50 on showers for friends. The amount you spend depends only on what you can afford and how close you are to the couple.
Some people only use the registry, some people find their own gifts. The only gift that wasn't appreciated was the one that had obviously been "regifted". THAT was REALLY tacky.
On hosting, whether it's a work shower or not: if you're the hostess, you host the shower (meaning pay for it). It is kinda tacky to "pass the hat" to cover expenses. If you need help with it, have a co-host or two, or do a smaller shower. But it's not polite to ask people to pay their own way to an event where there expected to bring a present, too.....
As for whether you can bring gifts to the wedding...yes, I've seen Miss Manners say it's tacky due to the hardship placed on the couple. But I don't think it's as big a crime as she makes it out to be.... I *do* admit, however, that we REALLY appreciated that most people sent them to our parents' homes in the weeks before the wedding. We moved the week we got back from the honeymoon, and it was just one less thing for us to worry about. The parents brought them down when they came to see the new place. So nice and convenient.... And that's why I order off the registry and have it mailed to the couple about 2-4 weeks before the wedding.
Just my 2 cents...take it for what it's worth.